Amplifier circuits



July 14,, i925. 1,545,855

7 E. o. SCRHVEN AMPLIFIER CIRCUITS Filed July 29, 1924 2 Sheets-Sheet 1I 3o 94/ 2590 I 5270 no oo 20 00 5600 fie uem lm/emfor: ah 4rd 050W? Junm W25, 1,545,855

' E. O. SCRIVEN AMPLIFIER CIRCUITS Filed July 29, 1924 2 Sheets-Sheet 2Patented July 14, 1925.

UNITED STA ES PATENT OFFICE.

EDWARD O. SCRIV'EN, OF NEW YORK, N. Y.. ASSIGNOR TO WESTERN ELECTRICCOM- 'PANY, INQORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

AMPLIFIER omcuirs.

Application filed July 29, 1924. Serial No. 728,880.

T 0 all whom it may concern:

Be it known that I, EDWARD O. SCKIVEN, a citizen of the United States ofAmerica, residing at New York city, in the county of New York and Stateof New York, have invented certain new and useful Improvements inAmplifier Circuits, of whichthe following is a full, clear, concise, andexact description.

This invention relates to electric amplifiers. It has for an object toobtain a constant direct current potential for the control electrode ofa repeater or electric discharge device without requiring the use of aspecial battery for that purpose.

This application is a continuation in art of my application Serial No.609,985, led

on December 30, 1922.

As is well known in the art, electric discharge devices, when used forexample as amplifiers or repeaters, are frequently employed in circuitsin which it may be found desirable to maintain a constant direct currentpotential difference between the control electrode and the cathode,whereby more satisfactory repeating or amplification may be obtaine Inaccordance with this invention as hereinafter described in detail animpedance element such as a resistance is placed 'in'the space currentpath of the amplifier between the cathode and the negative terminal ofthe source of voltage supplying space current to the repeaters, and thecontrol electrode is connected to that terminal of the resistanceadjacent to the negative end of the battery. This arrangement makes thecontrol electrode negative with respect to the cathode, which is thearrangement desired in most instances. However, a resistance connectedin this way produces coupling between the plate and grid circuits whichresults in a feed-back of energy through the tube in such a direction asto oppose normal amplification' In order to reduce this coupling for thefrequencies to be amplified it will generally be preferable to shunt thealternating current around the resistance by a shunting condenser, forexample. Though this arrangement aids in reducing the coupling, there isvery likely to'be considerable feed-back, particularl at low frequenciesto which a condenser 0 any but a very high capacity offers anappreciable impedance.

This will result in the lower frequenoiesbelng inefficiently transmitteOne feature of this invention comprises, the use of a phase reversingnetwork between the common impedance and the grid in order to producecoupling of aiding, polarlty.

Another feature of the invention comprises the use of a tertiarywindin-gon the input transformer for introducing a feedback tocompensate for the reverse phase coupling of the resistance common tothe grid and plate circuits.

In accordance with another feature of this invention the amplificationcharacteristic of the multi-stage amplifier employing a resistance.common to the plate and grid circuits is controlled by means of thecoupling afforded by the inter-stage transformers and a condenser orother circuit having an iin vpedance which is variable with frequency inshunt to the resistance. 4

These and other features of the invention can be morev clearlyunderstood by reference to the following description in connection withthe drawing which shows diagrammatically several embodiments of theinvention: Fig. 1 shows a single stage amplifier employing, inaccordance with the invention, a tertiary winding on the inputtransformer for producing a compensating feed-back. Fig. 2 shows a'single stage amplifier employing a phase reversing network.

Fig. 3 shows a multi-stage amplifier which employs a resistance in theplate battery circuit for obtaining a' negative grid potential in onlythe last stage.

Fig. 4.- shows a .multi-sta e amplifier in which a negative potential orgrids of all the stages is obtained from a common plate battery.

Fig. 5 is a curve showing the amplification frequencycharacteristics ofthe amplifier of Fig. 3, and

Fig. 6 shows a multi-stage amplifier employingv two tubes in push-pullrelation in the last stage, the grids of. which are maintained atanegati-ve potential by means of 'a resistance common to the plate and"grid circuits.

Referring to Fig. 1, the vacuum tube ampli'fier 7 is rovided, as usual,with a filament 8, gri 9, and plate 10. The filament former 6, battery16, resistance 15 to the cathode 8. The space current of the tube must,therefore, flow through resistance 15 producing a voltage drop therein.The control elect-rode being connected to the most negative end will bemore negative than the cathode by an amount equal to the IR drop in theresistance. In order to prevent a variation in the grid potential due tothe alternating current also flowing through the resistance; in otherwords, to reduce the coupling between the plate and grid circuits forthe frequencies to be transmitted, a condenser 17 is shunted across theresistance so by the common resistance 15, a

as to bypass the alternating current. However, in most cases thecondenser will not eliminate all the coupling between the plate and gridcircuits since 1t offers an appreciable impedance to the lowerfrequencies. A tertiary winding 18 is, therefore, provided on thetransformer 13 and connected across the resistance.15 in such adirection that the voltage which is induced in the secondary 14 is inphase with the voltage induced therein by the winding 12. In this way,the opposing coupling produced by the resistance 15 and the condenser 17is compensated or may even be overcompensated and a boosting efi'ectproduced at the low frequencies as is described more in detail inconnection with the circuit of Fi 3.

In the arrangement of Fig. 2, 1n order to reverse the phase of thecouplin caused high capacity condenser 19 is connected in the circuitbetween the secondary winding 14 and the negative terminal of batte 16.This condenser is shuntedby a very igh resistance 20 so as to provide aconductive path to keep the grid at a negative potential while offeringa prohibitive impedance to alternating currents.

Referring to Fig. 3, the two-stage amplifier comprises the vacuum tubes21 and 23 coupled together .by an inter-stage transformer 22. Thecathodes 24 and 25 are connected in series with a battery 26 whichsupplies filament heating current. Energy to be amplified is impressedon the circuit through an input transformer 27. One

. terminal of the secondary of transformer 27 is connected to the grid28 of the vacuum tube 21. The other terminal is connected to the cathodeat a point 29 which is directly connected to the negative terminal ofthe battery 26 so that the grid 28 is maintained at a. negativepotential with respect. to the cathode 24 by-the IR drop through cathode25. A battery 30 is used for supplying the space current to both tubes.The output circuit of the tube 21 may be traced from its plate 31through the primary 32 of the transformer 22, battery 30 and resistance33 to cathode 24. The input circuit of tube 22 may be traced from thegrid 34 through the secondary 35 of the transformer 22, the resistance33 to the cathode 25. The

output-circuit maybe tracedfrom the anode 38 through the primary of theoutput transformer 39 battery 30 resistance 33 to cathode 25. v

The grid 34 is maintained at a negative potential by the IR drop inresistance 33. A condenser 36 is shunted across the resistance 33 so asto provide a by-pass for the alternating current. It may sometimes bedesirable to shunt this condenser across both the resistance and thebattery, as is indicated in Fig. 4 to be described hereinafter. Thecurrent can be traced from the terminal 40 of the resistance 33 tocathode 24, across the space within the vacuum tube to the anode 31,through the primary winding 32, battery 30 (which acts as a conductorfor the alternating current) to, the other terminal' il of theresistance 33. Thepotcntial drop in the resistance is, therefore,impressed on the input terminals of the tube 23 through the transformer22 the primary 32 operating in a similar manner to the tertiary Winding18 in the circuit shown in Fig. 1. By properly poling this winding itis, therefore, possible to produce an aiding feed back proportional tothe drop across the resistance and condenser.

Referring to Fig. 5 in Which'the coordinates represent gain in miles andthe abscissae frequency on a logarithmic scale the group of curves Ashow the amplification of the am lifierin Fig. 3 when the winding 32 isoled so as to produce aidingcoupling and t e group B for opposingcoupling;

The curvesof each group represent the amplification with shuntingcondensers of various capacities as indicated on the curve. Comparisonof these curves shows that when the primary 32 is poled to produceopposing couplings, theamplification is low and falls off very rapidlyat the lower frequencies,

even if the shunting condenser has a capam a wide ran e of frequenciessuch as was obby using too low a capacity too great a feed back isobtained which is, likely to result in SlIlglIlQ.

- In the circuit of Fig. 3, when using a 60 volt battery in the platecircuit of the second tube the resistance 32 was adjusted to -3,000ohms, and shunted by a 0.3 m. f. condenser to give the best results.

The circuit shown in Fig. 4 is similar to that shown in Fig. 3 exceptthat the grid 28 of the first tube is also maintained at a negativepotential by the RI drop in resistance 33. This is provided for by anadjustable tap 42. By adjusting this tap any required negative voltagemay be supplied to the grid 28. Much more pronounced efiects repeater51, and in the third stage twocan be obtained with this circuit thanwith the circuit shown in Fig. 3.

Fig. 6 shows a three-stage amplifier comprising in the first stage avacuum tube repeater 50, in the second stage a vacuum tube yacuum tuberepeaters 52 and 53 connected in push-pull relation. The input circuitof the repeater 50 is coupled to the telephone transmitter 54 by asuitable transformer 56.

The output circuits of the tubes 52 and 53 are coupled to a receivingdevice 57, such .as a loud speaking telephone receiver bya suitableoutput transformer 55; The four cathodes 59, 60, 61 and. 62 are suppliedwith i heating current from a source of voltage 63.

A suitable source of voltage 64 is employed for supplying space currentto all the stages.

The grids of the first two tubes, and 51, are maintained at negativepotentials by means of resistances 65 and 66 included in the cathodecircuits. The resistance 67 is I included in the plate'circuits' of allthe tubes resistance 67 adjacent the negative terminal and the controlelectrodes of the tubes 52 and 53 are connected to the'terminal of theof the battery 64, whereby the'resistance 67 is included in theinput-circuits of the tubes 52 and 53. as well [as in their outputcircuits so that the gridsof these tubes aremaintained at negativepotentials with respect .to their cathodes by an amount depending on theIR drop in resis'tance67 in a similar Inannerto that of the amplifiersshown in the other figures. This potential di'fi'erence acrosstheterminals of resistance 67 is in addition to the potentialdifferences produced by the low resistances 7.0 and 71 in the filamentheating.circuitsywhereby the control electrodes of tubes 52 and 53 aremaintained more negative than the corresponding control electrodes oftubes 59 and 60. This arrangement isparticularly dcsirable since agreater grid cathode voltage is impressed upon tubes 52 and 53 than isimpressed upon the preceding tubes. As shown in the drawing, the fullpotential of battery 64 is impressed between the cathodes and anodes oftubes 50, 51, 52 and 58, exce t for the )otential dro in resist- 1 P l Ppling effect of the resistance.

It is to be understood that this invention may possess embodimentswidely different from the particular circuit arrangement above describedwithout departing in any way from the spirit of this inventionas'defined in the appended claims.

What is claimed is:

1. In an amplifier comprising an electron discharge device having acathode, a grid and an anode, a source of space current and an impedancecommon to the anode and grid circuits for maintaining the grid at afixed potential with respect to the cathode, means for controlling the vanode-grid coupling effect of said impedance, comprising circuitarrangements for impressing upon'the grid an electromotive forceopposite m phase to the electromotive force impressed upon the grid bythe coupling efl'ect of said impedance.

2. In an amplifier comprising an electron discharge device having acathode, agrid and an anode, a source of direct current potentialassociated with the anode circuit. and a resistance common to the anodeand grid circuits for. maintaining the grid at a negative potential withrespect to the cathode, a circuit having an impedance variable withfrequency shunting said resistance, and means for controlling theamplification of low frequencies comprising circuit arrangementsforimpressing on the grid an alternating electromotive force opposite inphase to that which is impressed by the natural coupling effect of saidresistance .and said shunting circuit. j

3. In'an amplifier comprising an electron discharge device having acathode, a grid and an anode, a source of potential associated with theanode-cathode circuit, and a resistance common to the grid and anodecircuits for maintaining the grid at a negative potential with respectto the cathode, means for controlling the frequency-amplificationcharacteristic of the amplifier comprising a circuit having an impedancevariable with frequency connected in shunt to said resistance andtransformer means -for impressing on the grid an electromotive forceopposite in phase and proportional to the electromotive force impressedthereon by the natural coupling effect of said resistance and shuntcircuit.

5. In a multi-stage amplifier, a plurality of electron discharge deviceseach having a cathode, a grid and an anode, a common source of spacecurrent for said devices, an impedance common to the grid and anodecircuits of one of said devices for maintaining the grid of said deviceat a negative potential with respect to the cathode, and transformermeans for impressing upon the grid an electromotive force opposite inphase to that which is impressed by the coupling effect of saidimpedance.

6. In a multi-stage amplifier, an electron discharge device having acathode, a grid and an anode in each stage, a common source ofanode-cathode potential for a plurality of stages, an impedanceconnected between the negative terminal of said source of potential andthe cathode of at least one of the stages, connections from the terminalof said impedance adjacent to the negative terminal of said source ofpotential to the grid of one stage, connections from said impedance tothe anode-cathode circuit of the preceding stage and a transformer forconnecting said two stages having such a polar ity that the secondarytermlnal connected to the grid of said first mentioned stage is ofapposite polarity to the primary terminal connected to the anode of saidpreceding stage.

7. A multi-stage set comprising an electric discharge device in eachstage having an anode, a cathode, and a control electrode, a commonsource of voltage connected to the anode and cathode of a plurality ofstages for supplying space current to said devices, an impedancetraversed bycurrent from said source, a connection between'the controlelectrode of one device and the cathode of said one device, saidconnection including at least a portion'of said impedance, and means forpreventing said control electrode connection from causing said set tosin.

8. A multi-stage set comprising an e ectric discharge device in eachstage having an anode, a cathode, and a control electrode, a commonsource of voltage connected to the anode and cathode of a plurality ofstages for supplying space current to said devices, an impedancetraversed by current from said source, a connection between the controlelectrode of one device and the cathode of said one device, saidconnection including at least a portion of said impedance, and means forby-passing alternating currents around said impedance.

'9. A multi-stage set comprising an electric discharge device in eachstage having an anode, a cathode, and a control electrode, a commonsource of voltage connected to the anode and cathode of a plurality ofstages for supplying space current to said devices, a resistancetraversed by current from said source, a connection between the,

controlfelectrode of one device and the cathode of said one device, saidconnection including at least a portion of said resistance and acondenser of large capacity connected effectively in shunt to saidresistance...

10. A multi-stage repeater set comprising a vacuum tube amplifier ineach stage having an anode, a cathode and a control elec-- trode, acommon source of voltage connected to the anode and the cathode of aplurality of the stages for supplying space current to said devices, aresistance connected .between said cathodes and the negative terminal ofsaid source and arranged to be traversed by the space current from saidsource, a. connection between the control electrode of a device in astage of said set subsequent to the first and the cathode of the saidone amplifier, said connection including said resistance,'and acondenser of.

large capacity connected effectively in shunt to said resistance.

11. A multi-stage set comprising an electric discharge device in eachstage having an'anode, a cathode, and a control electrode, a commonsource of voltage connected to the anode and cathode of a plurality ofstages for supplying space current to said devices, an impedancetraversed by current from said source, a connection between the controlelectrode of one device and the cathode of said one device, saidconnection including at least a portion of saidimpedance, and meanslowerlng the impedance across said portion for preventing said controlelectrode connection from causing said set to sing. I

In witness whereof, I hereunto subscribe my name this 25th day of JulyA. D., 1924.

- EDWARD O. SCRIVEN.

